Florida Secretary of State Ken Detzner on Thursday demanded that U.S. Sen. Bill Nelson, D-Fla, back up an “unsubstantiated” claim that Russians are hacking state voting systems.

“We are aware of the threat and the need to stay vigilant, but if you have specific information on a confirmed intrusion of any of Florida’s voting system or databases at the state or county level, we urgently need you to disclose that information to us so we can take action,” Detzner wrote in a letter with Okaloosa County Supervisor of Elections Paul Lux, the president of the Florida State Association of Supervisors of Elections.

The letter, which requested a reply “no later than Friday,” is the latest back and forth since Nelson, the ranking member of the U.S. Armed Services Committee’s Subcommittee on Cybersecurity, told reporters Aug. 7 in Tallahassee that, “The Russians are in Florida’s election records” and that they had “penetrated” some voter-registration systems.

When pressed, Nelson, said details of the information remained “classified.”

Some election information was targeted by hackers in 2016, and Nelson’s comments came as he said local election officials could get federal help to secure their databases and records from Russian cyber-hacking.

Since then, Nelson has told supporters that his comments simply repeated concerns he had been asked by Senate Intelligence Committee leaders to jointly convey with U.S. Marco Rubio, R-Fla., to elections officials regarding Russian interference.

Detzner is the chief elections official under Gov. Rick Scott, who is running against Nelson this fall.

Scott has repeatedly lashed out at Nelson about the assertions of Russian hacking.

Detzner wrote in Thursday’s letter that he would like a reply by Friday because of the start of statewide early voting on Saturday.